Integrated circuitry utilizes circuit devices. Example devices are transistors, and such may be used in numerous applications, including, for example, memory, logic, etc. Example transistors are PMOS (p-type metal oxide semiconductor) and NMOS (n-type metal oxide semiconductor). In some applications, a PMOS transistor may be utilized in combination with an NMOS transistor to form CMOS (complementary metal oxide semiconductor).
It is desired to develop transistors having suitable values of threshold voltage (VT) and sub-threshold voltage (SVT), high drive current (IDS), and low enough device off current (IOFF) for utilization in high-performance integrated circuitry. The sum of the contact resistance (RCS) between source/drain regions and conductive interconnects, and series resistance in source/drain regions (RSD), may limit IDS. For instance, RCS may become more and more dominated to limit IDS. RCS may be seriously degraded as devices are scaled down due to contact area decreasing as a function of square power on the scaling factor.
It is desired to develop new transistors which are suitable for utilization in high-performance integrated circuitry, and which are suitable for scaling into highly-integrated circuitry. It is also desired to develop new methods of forming transistors, and preferably to develop methods which reduce process steps as compared to conventional methods. It is further desirable for structures and methods to be extendible to devices other than transistors.